Electronic fuel injected internal combustion engines typically must maintain a minimum electrical power level to accurately deliver fuel to engine cylinders under high engine load operating conditions. In the event of a drop in engine control system electrical power, such as may be caused by a fault condition in an electric generator, fueling capacity reductions may occur, for example caused by a reduced operating level of popular electric fuel pumps the output of which varies with operating voltage, leading to lean cylinder air/fuel ratio conditions when high engine output power is demanded. Under high fuel flow conditions corresponding to high engine output power demands, an electric fuel pump that is operating under reduced drive voltage, may not be able to maintain fuel pressure within an acceptable pressure range. For example, the fuel pressure may drop by an order of magnitude or more, resulting in less fuel delivered to engine cylinders for given fuel injection commands, and lean air/fuel ratio conditions in engine cylinders. The lean air/fuel ratio conditions may reduce combustion quality in the engine, leading to potentially unpredictable loss of engine power. Under such conditions, unburned fuel may pass through the engine to catalytic treatment devices in the engine exhaust system and may damage the treatment devices, reducing their efficiency and adding to engine operating costs.
Conventional treatment of electrical system power reduction fault conditions takes the form of increasing engine speed to increase operating levels of electric generators. Such treatment does not address certain fault conditions in which the electric generator, or other electric system components have failed in such a manner that they are no longer responsive to increased engine speeds.
It would therefore be desirable to provide for engine control responsive to a loss of electric system power to preserve engine air/fuel ratio control precision and to ensure an adequate stable engine output with an air/fuel ratio supportive of efficient operation of catalytic treatment devices.